HvRRZ

by the way...Nobody... your avatar is awesome. Battle Royal is a great movie.

mxt_77

I like this answer. However, the description of the original post doesn't exactly match the symptoms that I usually hear associated with low tire pressures.

To the original poster, go try this: In a straight line on dry, even pavement, go about 30mph in 2nd gear, then floor it to get up to about 40, then lift off the throttle. If the car jerks one way or the other during acceleration or deceleration, then I would say that you should check your tire pressures (actually, I would say that you should check them anyway, just to rule that out). If the car doesn't pull one way or the other, then this seems to be symptomatic of something different.

To your other question... I'd say that downshifting when coming to a stop is not necessary. It adds wear to the clutch/syncros/engine/etc. It's cheaper & easier to replace brake pads than it is to replace engine & transmission goodies. However, it's personal preference, and I've never heard of somebody's clutch/syncros/etc failing just because they downshifted too much.

xviper

First, we haven't ascertained what the original posters meant by "jerking" or "squirrelly".
Second, in the very same example that you re-iterated, the revs are not going from our "hypothetical" 3500 rpm to 4200 rpm. If you let off the gas completely during a downshift and not touch it again till the clutch is re-engaged, the rpm starts at idle (less than 1000 rpm). So, the SUDDEN change in revs is not a simple 700 rpm as in your rebuttal but 3200 rpm. Please take note of Jackolope's second paragraph where he does in fact, mention "large rpm change".
Lastly, with such an abrupt change in rpm and the subsequent rear wheel lock, you get a weight transfer to the front, as you would in any "braking" of forward momentum (even without the use of the service brakes). This sudden forward weight transfer will cause a remarkable change in front end dynamics. Now, as far as "jerk" or "squirrelly" goes, this is a matter of individual interpretation and until the original poster explains what he meant, I shall say that this situation can make the front end "jerk".

ps. At no time has Jackolope stated that his car went to the side in such a fashion as to make it "hard to control". This, of course, is something that you read into his statement.

emrillive

this might be a newbie question, actually it is. ok it is about downshifting, is this the process of downshifting?

while on the gas clutch in and in the process of shifting down a gear also give it more gas to match the cars egine speed to the transmission higer rpm?

basically what i want to know is, while downshifting you never let off the gas right,you just give it more gas.

correct?

PezS2000

Keep the revs up and you will have a smooth transition from any downshift.

As for the clutch/brake question.....Spare the engine use the brakes, easier and cheaper to change brake pads than it is to replace a clutch, but it is more fun to down shift and hear the purrrrrr of the engine.

Use the engine for braking when engaged in heavy racing on a track, but be prepared to conduct regular engine rebuilds like the big boy racers.

Just have fun in a car that was built for enjoyment....racing or cruising!

jackalope

thanks for all the replies. I'll try rev matching, I get the feeling that that will fix the problems.

xviper

This depends on which scenario you are engaging in ..................................
1. Decelerating to the car: You are already off the gas, right? (Because you are in the process of slowing down.) You may also be using the brakes if you are trying to slow down a bit more rapidly but still not considered a "panic" stop. When it's time to shift, get off the brake (if you're on them or continue to use the brake but heel/toe) and prepare to blip the gas to an extent that will get you to the right rpm after the shift. Clutch in, shift and blip gas about the same time. You can do this very rapidly with practice. Release the clutch quickly before the revs come down. You should get to the point where this transition is seemless.

2. Emergency acceleration: Hold gas. The following is done very quickly: clutch in, shift, clutch out, mash the gas just before the clutch hits the top.

xviper

If the revs are matched precisely, there is minimal to no additional clutch wear. Clutch wear happens mainly when the separate rotating surfaces are slammed together at different rotating speeds. A proper rev match does just this. It "matches" the speeds of the input side of the clutch to the output side of the clutch. Surfaces mesh together going the same speed and hence does not rub each other with great friction.
As far as engine rebuilds go, unless you are subjecting the car to mechanical "over-revs", it should not cause any harm. An engine is there to take on the load of the weight of the car and to motivate it going faster. It does not experience any different loading when making the car go slower.